With reference to FIG. 1, a ducted fan gas turbine engine generally indicated at 10 has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake 11, a propulsive fan 12, an intermediate pressure compressor 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, and intermediate pressure turbine 17, a low-pressure turbine 18 and a core engine exhaust nozzle 19. A nacelle 21 generally surrounds the engine 10 and defines the intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.
The gas turbine engine 10 works in a conventional manner so that air entering the intake 11 is accelerated by the fan 12 to produce two air flows: a first air flow A into the intermediate pressure compressor 14 and a second air flow B which passes through the bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 13 compresses the air flow A directed into it before delivering that air to the high pressure compressor 14 where further compression takes place.
The compressed air exhausted from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the nozzle 19 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors 14, 13 and the fan 12 by suitable interconnecting shafts.
The combustion equipment 15 of such an engine typically has one or more combustion chambers, with fuel being delivered to the or each chamber by one or more fuel injectors.
As shown in FIG. 2, each fuel injector 24 is often mounted externally of a casing 25 of the combustion chamber 26 at a respective aperture through the casing. Each injector has a mounting flange 27 which is sealingly connected to the external surface of the casing with a feed arm 28 and tip 29 of the injector passing through the aperture and the tip engaging into the head 30 of the combustion chamber. Bolts 31 secure the flange via threads in the casing.
However, a problem with this arrangement is that the securing bolts 31 are working against the casing internal pressure. More particularly, the pressure difference across the casing 25 may be in the range from about 35 to 4100 kPa, with the high pressure within the casing forcing the injector flange 27 away from the casing. This can cause air leakage, and hence engine efficiency loss. On the other hand, an advantage of the arrangement is that the injector 24 can be removed on-wing for maintenance or replacement.
An alternative arrangement has the injector flange sealingly connected to the internal surface of the casing. This overcomes the air leakage problem because the sealing arrangement is working with the internal pressure, i.e. the pressure difference across the casing forces the flange toward the casing. However, the internally mounted injector cannot be easily removed as the flange is too large to be withdrawn through the aperture. Thus the injector can only be removed from the inside, which requires a major engine strip, rendering on-wing maintenance or replacement effectively impossible.
Thus there is a need to provide a system for mounting a fuel injector to a gas turbine engine which facilitates on-wing removal of the injector while reducing air leakage.